Use the position of the Kafka Consumer to track progress instead of Consumer Records offsets

Kafka Partitions with transactional messages (post 0.11) will include commit or abort markers which indicate the result of a transaction. The markers are not returned to applications, yet have an offset in the log. Therefore the end of Stream position can be the offset of a control message.
This Patch change the way how we keep track of the consumer position by using

 consumer.position(topicP) 

as oppose to using the offset of the consumed messages.
Also I have done some refactoring to help code readability hopefully.